Scale inhibitors

ABSTRACT

The invention relates to the inhibition of tripolyphosphate and pyrophosphate scales in aqueous systems involving adding to said aqueous system at least one copolymer comprising the following monomers in polymerized form: 
     (I) 50-80% by weight of one or more weak acids; 
     (II) 2-50% by weight of one or more strong acids; 
     (III) 0-30% by weight of one or more monoethylenically unsaturated C 4 -C 8  dicarboxylic acids; and 
     (IV) 0-30% by weight of one or more monomethylenically unsaturated monomers polymerizable with (I), (II) and (III); 
     wherein the total of monomers (I), (II), (III), and (IV) equals 100% by weight of copolymer. 
     The invention is particularly suited to the inhibition of tripolyphosphate and pyrophosphate scales which occur as a result of using low phosphate (STPP) containing detergent formulations.

This Application is a continuation of Ser. No. 09/071,025, filed May 1, 1998, now U.S. Pat. No. 6,114,294.

The present invention relates to the inhibition of (poly)phosphate salt scale in aqueous systems.

It is well known that in hard water areas high concentrations of magnesium and calcium ions can lead to the formation of insoluble calcium and magnesium carbonate deposits (scaling) on washed articles. This is visible, as a white deposit, particularly on glassware when such articles, are washed in automatic dishwashing machines, and also on machine parts especially heater elements. Similar precipitation problems also occur in laundry washing, these cause the fabric to become stiff and rough to the touch and give coloured fabrics a faded appearance. Tap water with relatively high water hardness and the use of insufficient water softening chemicals increase the problem dramatically. Other factors involved in causing scaling are temperature (more scaling occurs at higher temperatures) and pH (higher pH also increases scaling). Since the mid 1960's, sodium tripolyphosphate (STPP) has been used in large quantities in most detergent formulations as a “builder”; that is an agent which is able to sequester positive cations such as magnesium and calcium in the washing solution and prevent them from depositing as salts (carbonate, silicate etc.) on the items being washed.

However, it is now known that the presence of phosphate, for example in the form of STPP, in lakes and rivers serves as a nutrient for algae growth and this results in a deterioration of water quality. These environmental concerns have lead to the removal of STPP in detergent formulations and their replacement with other sequestering compounds. Unfortunately, the changes that occur in the washing process without inclusion of phosphate are more complex than those expected from the simple decrease in sequestration capacity of the detergent matrix. The multi-purpose capabilities of the STPP in the areas of emulsification of oily particles, stabilisation of solid soil suspension, peptisation of soil agglomerates, neutralisation of acid soils, etc. are all key to obtaining an excellent wash end result.

To try to maintain as many of the desirable properties of STPP as possible, whilst at the same time limiting its environmental impact, reduced STPP levels are used. However, this in itself brings new scaling problems. When high levels of STPP are used in the wash bath of dishwashing and laundry washing machines, the predominant species formed in the aqueous system is a water soluble 1:1 metal ion:STPP complex (eg. CaP₃O₁₀ ⁻³). As STPP levels decrease, water insoluble calcium and magnesium salts of tripolyphosphate (eg. Ca₅(P₃O₁₀)₂) and pyrophosphate (eg. Ca₂P₄O₇) are formed which consequently precipitate from the aqueous system.

Prior art documents are known, for example U.S. Pat. No. 3,806,367, U.S. Pat. No. 3,928,196, and U.S. Pat. No. 3,898,037, which address the problem of controlling scale in STPP free systems. However, there is no teaching of any effective way to control the (poly)phosphate scales which are formed using low-STPP levels (ie. through the use of “Ultra” or “Compact” detergent formulations) where the concentration of the STPP in the wash bath is, for example, below 1500 ppm. The precise amount of scale observed will depend upon the concentration of divalent cation in the wash bath. For comparison, typical high-STPP wash bath concentrations in current commercial use, have greater than 2000 ppm of STPP.

The term “(poly)phosphate scale” used herein refers to phosphate, tripolyphosphate and pyrophosphate scales collectively. Also, the term “copolymer” is used to mean polymers containing at least one strong acid and at least one weak acid, as well as polymers containing one or more additional types of monomers.

The problem addressed by the present invention, therefore, is to provide a method of controlling (poly)phosphate salt scale in aqueous systems and to also provide detergent formulations which have good anti-filming performance characteristics when used in machine dishwashing detergents and good anti-encrustation and anti-deposition performance characteristics when used in laundry washing detergents.

Accordingly, the present invention provides a method of controlling (poly)phosphate scale comprising treating the aqueous system with at least one copolymer comprising the following monomers in polymerized form:

(I) 50-98% by weight of one or more weak acid;

(II) 2-50% by weight of one or more strong acid;

(III) 0-30% by weight of one or more monoethylenically unsaturated C₄-C₈ dicarboxylic acid; and

(IV) 0-30% by weight of one or more monoethylenically unsaturated monomers polymerizable with (I), (II), and (III);

wherein the total of monomers (1), (II), (III) and (IV) equals 100% by weight of copolymer.

The invention further provides a method of controlling (poly)phosphate scale in aqueous systems comprising treating the aqueous system with at least one copolymer comprising polymerized units of the following polymers:

(I) 50-98% by weight of one or more monoethylenically unsaturated C₃ to C₆ monocarboxylic acid;

(II) 2-50% by weight of one or more unsaturated sulphonic acid;

(III) 0-30% by weight of one or more monoethylenically unsaturated C₄ to C₈ dicarboxylic acid;

(IV) 0-30% by weight of one or more monoethylenically unsaturated monomer polymerizable with (I), (II) and (III); wherein the total of monomers (I), (II), (III) and (IV) equals 100% by weight of the copolymer.

Preferably, the copolymer comprises polymerized units of the following monomers:

(I) 50-90% by weight of one or monoethylenically unsaturated C₃-C₆ monocarboxylic acid;

(II) 10-50% by weight of unsaturated sulphonic acid;

(III) 0-30% by weight of one or more monoethylenically unsaturated C₄-C₈ dicarboxylic acid; and

(IV) 0-30% by weight of one or more monoethylenically unsaturated monomer polymerizable with (I), (II) and (III), wherein the total of monomers (I), (II) (III) and (IV) equals 100% by weight of the copolymer.

Advantageously, the copolymer of the present invention comprises polymerized units of the following monomers:

(I) 60-90% by weight of one or monoethylenically unsaturated C₃-C₆ monocarboxylic acid

(II) 10-40% by weight of unsaturated sulphonic acid.

(III) 0-30% by weight of one or more monoethylenically unsaturated C₄-C₈ dicarboxylic acid; and

(IV) 0-30% by weight of one or more monoethylenically unsaturated monomer polymerizable with (I), (II) and (III), wherein the total of monomers (I), (II) (III) and (IV) equals 100% by weight of the copolymer.

A copolymer with particularly good (poly)phosphate scale inhibition properties comprises polymerized units of the following monomers:

(I) 77% by weight of one or monoethylenically unsaturated C₃-C₆ monocarboxylic acid

(II) 23% by weight of unsaturated sulphonic acid.

The monoethylenically unsaturated C₃-C₆ monocarboxylic acid is preferably (meth)acrylic acid.

The unsaturated sulphonic acid monomer is preferably one of the following: 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-methacrylamido-2-methyl-1-propanesulphonic acid, 3-methacrylamido-2-hydroxy-propanesulphonic acid, allylsulphonic acid, methallylsulphonic acid, allyloxybenzenesulphonic acid, methallyloxybenzenesulphonic acid, 2-hydroxy-3-(2-propenyloxy)propanesulphonic acid, 2-methyl-2-propene-1-sulphonic acid, styrene sulphonic acid, vinylsulphonic acid, 3-sulphopropyl acrylate, 3-sulphopropyl methacrylate, sulphomethylacrylamide, sulphomethylinethacrylamide, and water soluble salts thereof.

The monoethylenically unsaturated C₄-C₈ dicarboxylic acid is preferably maleic acid, and the monoethylenically unsaturated monomer polymerizable with (I), (II) and (III) is preferably selected from one or more of C₁-C₄ alkyl esters of (meth)acrylic acid; C₁-C₄ hydroxalkyl esters of (meth)acrylic acid; acrylamide; alkyl substituted acrylamide, N,N-dialkyl substituted acrylamides; sulphonated alkyl acrylamides; vinylsulphonates; vinyl sulphonic acid. (meth)allylsulphonic acid; vinylphosphonic acid; vinyl actetate; allyl alcohols; sulphonated allyl alcohols, acylonitrile; N-vinylpyrrolidone; N-vinylformamide; N-Vinylimidazole; and N-vinylpyridine.

The weight average molecular weight of the copolymer according to the present invention is from 3,000 to 50,000 and preferably from 4,500 to 35,000.

The present invention also provides a detergent formulation comprising at least one copolymer comprising polymerized units of the following monomers:

(I) 50-98% by weight of one or more monoethylenically unsaturated C₃ to C₆ monocarboxylic acid;

(II) 2-50% by weight of one or more unsaturated sulphonic acid;

(III) 0-30% by weight of one or more monoethylenically unsaturated C₄ to C₈ dicarboxylic acid;

(IV) 0-30% by weight of one or more monoethylenically unsaturated monomer polymerizable with (I), (II) and (III); wherein the total of monomers (I), (II), (III) and (IV) equals 100% by weight of the copolymer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the inhibition of calcium tripolyphosphate as a function of AMPS comonomer concentration.

FIG. 2 shows the inhibition of calcium tripolyphosphate as a function of AMPS comonomer concentration and molecular weight.

FIG. 3 shows the inhibition of calcium tripolyphosphate as a function of maleic comonomer concentration and molecular weight.

FIG. 4 shows the inhibition of calcium tripolyphosphate by an AMPS containing terpolymer as a function of a “hydrophobic” comonomer.

FIG. 5 shows the inhibition of calcium tripolyphosphate by an AMPS containing terpolymer as a function of molecular weight.

FIG. 6 shows the effect of various polycarboxylates on film inhibition.

The invention will now be further illustrated by the following examples.

General Screening Method

Polymers according to the present invention were evaluated for calcium tripolyphosphate precipitation inhibition in a phosphate containing automatic dishwashing detergent formulation, and by titrating a 750 ppm STPP solution with incremental levels of water hardness (2/1 Ca⁺/Mg⁺⁺) at elevated temperatures (55° C.) and a fixed polymer concentration (100 ppm). The onset of turbidity was measured utilizing a Brinkmann PC 701 Probe Colorimeter (520 nm), and the experiment was concluded with the observation of a visible precipitate.

Detergent Formulations

TABLE 1 Detergent Formulations Det. Form 1 Det. Form 2 Concentration Concentration Component (%) (%) STPP 20.0 35.0 Soda Ash 30.0 22.0 Sodium disilicate (Britesil H20) 12.0 12.0 Sodium citrate dihydrate 10.0 — Sodium perborate 4H₂O 7.5 7.5 Bleach activator (TAED)* 2.5 2.5 Surfactant (SLF-18) 3.5 3.5 Protease 1.0 1.0 Amylase 0.5 0.5 Sodium sulphate 9.0 14.0 Polymer 4.0 2.0 *TAED is tetra acetyl ethylene diamine

Detergent formulation 1 is a low STPP containing formulation whereas detergent formulation 2 contains a high percentage of STPP.

Key to acronyms used herein:

Mw=weight average molecular weight. All molecular weights quoted are weight average molecular weight unless otherwise specified.

AA =Acrylic acid

Mal=Maleic acid

AMPS=2-acrylamido-2-methyl-1-propanesulphonic

TBAM=tertbutylacrylamide

TOAM=tertoctylacrylamide

DMAM=Dimethylacrylamide

EA=Ethyl acrylate

HPA=Hydroxypropyl acrylate

STY=Styrene

SMAS=Sodium methallyl sulphonate.

MAA=Methylacrylic acid.

Dishwashing Conditions

The anti-filming performance in dishwashing applications of polymers according to the present invention were also tested using conventional procedures; under one or either of the following conditions, (A) or (B):

(A) US Washing Conditions

Dishwashing machine: Whirlpool model DU 940

Water Hardness: 300 ppm as calcium carbonate (Ca/Mg=3.5:1)

No food soil

Normal Programme (50° C.)

No Rinse Aid

Dishwares: glasses

Cycles: 5

Filming Scores: 0.0 = No visible film 2 = Intermediate 0.5 = Barely Perceptible 3 = Moderate 1.0 = Slight 4 = Heavy

(B) European Washing Conditions

Dishwashing machine: Miele Deluxe model G590 SC

Water Hardness: 600 ppm as calcium carbonate (Ca/Mg=3.5:1)

No food soil

Normal Programme (65° C.)

No Rinse Aid

Dishwares: glasses

Cycles: 5

Filming Scores: 0.0 = No visible film 2 = Intermediate 0.5 = Barely Perceptible 3 = Moderate 1.0 = Slight 4 = Heavy

EXAMPLE 1

The Effect of AMPS Containing Copolymer on the Inhibition of Calcium Tripolyphosphate

Copolymer containing solutions were evaluated according to the general screening method described above to give the results shown in FIG. 1. In summary, the calcium tripolyphospate antiprecipitation improves as the level of AMPS in the copolymer increases up to 50% AMPS, at levels greater than 50% AMPS, the inhibition of tripolyphosphate scale starts to decrease

EXAMPLE 2

The Effect of AMPS Containing Copolymer on Filming

Copolymers according to Example 1 were included in various automatic dish washing detergent formulations and were tested under wash conditions (A). Table 2 shows the glass filming scores obtained; these confirm the observation that increasing ANUS levels up to 50% increases inhibition of (poly)phosphate scale.

TABLE 2 Molecular Filming Score Filming Score Polymer Weight Det. Form 1 Det. Form 2 No Polymer — 3.5 3.0 100AA (Comparative) 2,000 1.5 1.75 100AA (Comparative) 4,500 1.1 2.0 90 AA/10 Mal (Comp) 3,200 1.3 1.75 80 AA/20 Mal (Comp) 16,000 1.2 1.3 70 AA/30 Mal (Comp) 30,000 1.0 2.0 50 AA/50 Mal (Comp) 3,500 1.1 1.2 50 AA/50 Mal (Comp) 25,000 1.1 2 30 AA/70 Mal (Comp) 5,500 1.4 1.2 95 AA/5 EA (Comp) 2,500 1.75 2.5 80 AA/20 EA (Comp) 4,300 1.25 1.1 70 AA/30 MAA (Comp) 3,500 1.1 1.0 77 AA/23 AMPS 4,500 0.5 0.6 60 AA/40 AMPS 10,000 0.5 0.3 77 AA/23 SMAS 6,600 0.8 0.9 60 AA/40 SMAS 3,870 0.3

EXAMPLE 3

The Effect of the Molecular Weight of AMPS Containing Copolymers on the Inhibition of Calcium Tripolyphosphate

FIG. 2 focuses on the effect of molecular weight of the copolymers at two different AA/AMPS molar ratios. In both cases, increasing the molecular weight of the copolymer significantly enhances the tripolyphosphate antiprecipitation properties of the copolymer. The particle size of the precipitated scale was visibly smaller (higher transmittance) with higher molecular weight analogues.

EXAMPLE 4

The Effect of AMPS Containing Terpolymers on the Inhibition of Calcium Tripolyphosphate

FIG. 3 shows that AA/AMPS/X containing terpolymer (where X is anther monomer unit which is not AA or AMPS) have a greater efficacy in (poly)phosphate scale inhibition with increasing, AMPS levels, when the polymers have similar molecular weights.

EXAMPLE 5

The Effect of Hydrophobically Modified AMPS Containing Terpolymers on the Inhibition of Calcium Tripolyphosphate

The desired inhibition of (poly)phosphate scale is also observed for AA/AMPS copolymers which have been modified by the incorporation of a third “hydrophobic” monomer; see the results illustrated in FIG. 4.

EXAMPLE 6

The Effect of Hydrophobically Modified AMPS Containing Copolymers on Filming

The results of Example 6 are also confirmed in Example 7, see Table 3 below.

TABLE 3 Molecular Filming Score Filming Score Polymer Weight Det. Form 1 Det. Form 2 No Polymer — 3.5 3.0 100 AA (Comparative) 4,500 1.1 2.0 90 AA/10 Mal (Comp) 3,200 1.3 1.75 70 AA/30 Mal (Comp) 30,000 1.0 2.0 50 AA/50 Mal (Comp) 25,000 1.1 2 30 AA/70 Mal (Comp) 5,500 1.4 1.2 95 AA/5 EA (Comp) 2,500 1.75 2.5 70 AA/30 MAA (Comp) 3,500 1.1 1.0 62 AA/23 AMPS/15 24,800 0.4 0.5 TBAM 64.5 AA/27 SMAS/8.5 5,130 0.8 TBAM 64.5 AA/27 SMAS/8.5 4,120 1.1 TBAM

EXAMPLE 7

The Effect of Molecular Weight On Hydrophobically Modified AMPS Containing Terpolymers on the Inhibition of Calcium Tripolyphosphate

Inhibition of (poly)phosphate scale also increases with increasing the molecular weight of AMPS containing copolymers which have been modified with a hydrophobic monomer. The results are shown in FIG. 5

EXAMPLE 8

The effect of Various Polycarboxylates on (Poly)phosphate Film Inhibition Using Conditions (B)

A solution containing 15 g/dosagewash of 77AA/23 AMPS (Mw 4,500) copolymer was tested under wash conditions (B) and the inhibition results were compared against those obtained by testing under the same conditions for solutions containing one of 70AA/30 MAL (Mw 30,000), 100% pAA (Mw 4,500) and a control solution which did not contain any polymer. The results shown in FIG. 6 indicate a dramatic increase in (poly)phosphate scale inhibition using the copolymer comprising 77AA/23 AMPS. 

We claim:
 1. Method of controlling poly(phosphate) scale in aqueous systems comprising adding to the aqueous system at least one copolymer comprising polymerized units of the following monomers: (I) 50-98% by weight of one or more weak acids selected from the group consisting of monoethylenically unsaturated C₃ to C₆ monocarboxylic acid; (II) 2-50% by weight of one or more unsaturated sulfonic acid selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-methacrylamido-2-methyl-1-propane-sulfonic acid, and water soluble salts thereof; (III) 0-30% by weight of one or more monoethylenically unsaturated C₄-C₈ dicarboxylic acid; and (IV) 0-30% by weight of one or more monoethylenically unsaturated monomers polymerizable with (I), (II) and (III); wherein the total of monomers (I), (II), (III) and (IV) equals 100% by weight of copolymer; wherein the aqueous system contains sodium tripolyphosphate in an amount not to exceed 1500 parts per million; and further wherein the scale being controlled is selected from the group consisting of tripolyphosphate and pyrophosphate.
 2. Method according to claim 1 wherein the copolymer comprises polymerized units of the following monomers: (I) 50-90% by weight of one or more weak acids selected from the group consisting of monoethylenically unsaturated C₃-C₆ mono-carboxylic acid; (II) 10-50% by weight of one or more unsaturated sulfonic acid selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-methacrylamido-2-methyl-1-propanesulfonic acid, and water soluble salts thereof; (III) 0-30% by weight of one or more monoethylenically unsaturated C₄-C₈ dicarboxylic acid; and (IV) 0-30% by weight of one or more monoethylenically unsaturated monomer polymerizable with (I), (II) and (III).
 3. Method according to claim 1 wherein the copolymer comprises polymerized units of the following monomers: (I) 60-90% by weight of one or more monoethylenically unsaturated C₃-C₆ monocarboxylic acid; (II) 10-40% by weight of one or more unsaturated sulfonic acid selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-methacrylamido-2-methyl-1-propane-sulfonic acid, and water soluble salts thereof; (III) 0-30% by weight of one or more monoethylenically unsaturated C₄-C₈ dicarboxylic acid; and (IV) 0-30% by weight of one or more monoethylenically unsaturated monomer polymerizable with (I), (II) and (III).
 4. Method according to claim 1 wherein the monoethylenically unsaturated C₃-C₆ monocarboxylic acid is selected from the group consisting of one or more of acrylic acid and methacrylic acid.
 5. Method according to claim 1 wherein the monoethylenically unsaturated C₄-C₈ dicarboxylic acid is maleic acid, and the monoethylenically unsaturated monomer polymerizable with (I), (II) and (III) is selected from the group consisting of (C₁-C₄)alkyl esters of (meth)acrylic acid, (C₁-C₄)hydroxalkyl esters of (meth)acrylic acid, acrylamide, alkyl substituted acrylamide, N,N-dialkyl substituted acrylamides, sulphonated alkyl acrylamides, vinylphosphonic acid, vinyl acetate, allyl alcohols, sulphonated allyl alcohols, acrylonitrile, N-vinylpyrrolidone, N-vinylformamide, N-vinylimidazole and N-vinylpyridine.
 6. Method according to claim 1 wherein the weight average molecular weight of the copolymer is from 3,000 to 50,000.
 7. Method according to claim 1 wherein the copolymer comprises: (a) 77% by weight of acrylic acid; and (b) 23% by weight of 2-acrylamido-2-methyl-1-propanesulphonic acid.
 8. Method according to claim 1 wherein the copolymer is added to a machine dishwashing and/or laundry detergent formulation used in the aqueous system and the aqueous system is a wash bath of a dishwashing and/or laundry washing machine.
 9. Method according to claim 1 wherein the copolymer consists essentially of polymerized units of the following monomers: (I) 60-90% by weight of one or more monoethylenically unsaturated C₃-C₆ monocarboxylic acid; and (II) 10-40% by weight of an unsaturated sulfonic acid selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-methacrylamido-2-methyl-1-propanesulfonic acid, and water soluble salts thereof.
 10. Method according to claim 1 wherein the copolymer consists essentially of polymerized units of the following monomers: (I) 62 to 65% by weight of one or more monoethylenically unsaturated C₃-C₆ monocarboxylic acid; (II) 23 to 27% by weight of an unsaturated sulfonic acid selected from the group consisting consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-methacrylamido-2-methyl-1-propanesulfonic acid, and water soluble salts thereof; and (III) 8 to 15% by weight of one or more monoethylenically unsaturated monomer polymerizable with (I) and (II). 